The present proposal addresses the question of how people comprehend sentences that they read or hear. Its long-range goal is to develop a theory of how people use knowledge of their language to structure world into mental representation that can then be interpreted semantically. The proposed research is designed to uncover the principles that govern readers' and listeners' use of grammatical information in sentence parsing, and is predicated upon the assumption that these principles will form a distinct subset of the principles that govern cognition in general. Three specific topics are addressed in the proposed research: (a) the applicability across languages of principles of phrase structure parsing we and our colleagues have identified in previous research; (b) the possible existence of differences in how argument phrases and adjunct phrases are parsed; and (c) the nature of the mental representation or representations of a sentence that are constructed during sentence comprehension. The research will use a variety of experimental techniques, testing normal adult humans on the speed with which they read sentences, the speed and accuracy with which they make judgments about sentences, and the effects that reading or hearing sentences have upon tasks performed concurrently with reading or listening. Our research is designed to contribute to the development of psycholinguistic theory. Recent advances in psycholinguistic theory have had a major impact on the analysis of language disorders, especially the aphasias. We look forward to the time when these new analyses will lead to improved treatments and we hope to contribute to the psycholinguistic theory that fuels the increase in our understanding of language disorders.